Method and arrangement for transmitting and receiving RF signals through various radio interfaces of communication systems

ABSTRACT

A method and arrangement for transmitting and receiving RF signals, associated with different radio interfaces of communication systems, employ a direct conversion based transceiver which substantially comprises one receive signal branch and one transmit signal branch. Mixing frequencies of the different systems are generated by a single common by use of an output frequency divider in combination with the synthesizer, and by use of filtering corresponding to a system channel bandwidth by means of a controllable low-pass filter operating at baseband frequency.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. application Ser. No.09/856,746 filed May 24, 2001, which is a U.S. national stage ofPCT/FI99/00974, filed on Nov. 25, 1999, which is based on and claimspriority to Finnish application no. 982559, filed on Nov. 28, 1998, allincorporated by reference herein.

The invention relates to a method and arrangement for transmitting andreceiving RF signals associated with various radio interfaces ofcommunication systems. The invention finds particular utility intransceivers of general-purpose mobile stations.

Mobile communication systems are developing and expanding rapidly whichhas led to a situation in which there are in many areas systemscomplying with several different standards. This has brought about aneed for mobile stations that can be used in more than one system. Goodexamples are the digital systems called GSM (Global System for Mobilecommunications) and DCS (Digital Cellular System), which operate ondifferent frequency bands but have otherwise similar radio interfaces.In addition, the modulation, multiplexing and coding schemes used may bedifferent. The systems mentioned above use the time division multipleaccess (TDMA) method; other methods include the frequency divisionmultiple access (FDMA) and code division multiple access (CDMA).

One possible way of making a mobile station capable of operating inmultiple systems is to have in the mobile station completely separatesignal paths for each system. This, however, would lead to anunreasonable increase in the mobile station size and manufacturingcosts. Therefore, the goal is to design a mobile station in which thedifferences relating to the radio interfaces of the various systemscould be largely dealt with by means of programming, instead of havingseparate signal processing paths.

It is known e.g. from patent application document EP 653851 atransceiver arrangement using one local oscillator the frequency ofwhich falls between the lower operating frequency band and the higheroperating frequency band such that one and the same intermediatefrequency (IF) can be used for both operating frequency bands. However,the disadvantage of such a solution is that the necessary IF stages makethe implementation rather complex, and the manufacturing costs of thedevice will be high because of the great number of components.Furthermore, the IF stages require filters in order to eliminatespurious responses and spurious emissions. In addition, channelfiltering at the intermediate frequency sets great demands on the IFfilters.

In a direct-conversion, or zero-IF, receiver the radio-frequency (RF)signal is directly converted into baseband without any intermediatefrequencies. Since no IF stages are needed, the receiver requires only afew components, therefore being an advantageous solution forgeneral-purpose mobile stations which have multiple signal branches fordifferent systems. To aid in understanding the problems relating to thedirect conversion technique and prior art it is next described in moredetail a prior-art solution.

FIG. 1 shows a direct conversion based arrangement for realizing a dualfrequency band transceiver, known from the Finnish Patent document FI100286. Depending on the receive frequency band, a RF signal received byan antenna is coupled by means of switch 104 either to a first receivebranch (DCS) or second receive branch (GSM).

If the received signal is in the DCS frequency band, it is conducted toband-pass filter 106, low-noise amplifier (LNA) 108 and bandpass filter110. After that the signal is brought to block 112 which produces signalcomponents having a 90-degree phase differences. The in-phase componentI and quadrature component Q are further conducted by means of switches114 and 134 to mixers 116 and 136. The mixers get their mixing signalsfrom a DOS synthesizer 140 the frequency of which corresponds to thereceived carrier frequency so that the mixing produces the in-phase andquadrature components of the complex baseband signal. The basebandsignal is further processed in the receive (RX) signal processing unit,block 139.

If the signal received is a USM signal, switch 104 directs the receivedsignal to the GSM branch which comprises, connected in series bandpassfilter 126, low-noise amplifier 128, bandpass filter 130 and phaseshifter 132 which generates two signals with a mutual phase differenceof 90 degrees. The signals are further conducted by means of switches114 and 134 to mixers 116 and 136 where the mixing frequency is nowdetermined by a signal coming from the GSM synthesizer 150 via switch161. The signals produced by the mixers are further conducted to thebaseband RX signal processing unit 139.

The DCS synthesizer comprises in a known manner a phase-locked loop(PLL) which includes a voltage-controlled oscillator (VCO) 141 theoutput signal of which is amplified at amplifier 146 thus producing thesynthesizer output signal. The frequency of the signal from oscillator141 is divided by an integer Y in divider 142 and the resulting signalis conducted to phase comparator 143. Similarly, the frequency of thesignal generated by reference oscillator 158 is divided by an integer Xin divider 144 and conducted to phase comparator 143. The phasecomparator produces a signal proportional to the phase difference ofsaid two input signals, which signal is conducted to a low-pass filter(LPF) 145 producing a filtered signal that controls thevoltage-controlled oscillator 141 The phase-locked loop described aboveoperates in a known manner in which the output frequency of thesynthesizer becomes locked to the frequency coming to the phasecomparator from the reference frequency branch. The output frequency iscontrolled by varying the divisor Y.

The GSM synthesizer 150 comprises a voltage-controlled oscillator 150,amplifier 156, dividers 152 and 154, phase comparator 153 and a low-passfilter 155. The GSM synthesizer operates like the DCS synthesizerdescribed above, but the output frequency of the GSM synthesizercorresponds to GSM frequency bands.

In the transmitter part, a baseband complex transmit (TX) signal isprocessed in a TX signal processing unit wherefrom the in-phase andquadrature components of the signal are conducted to mixers 162 and 182that produce a carrier-frequency signal by multiplying the input signalby the mixing signal. If the transmission is at the DCS frequency,switch 161 selects the DCS synthesizer's output signal as the mixingsignal. The carrier-frequency signal is conducted through switch 164 tothe DCS branch where a 90-degree phase shift is first produced betweenthe in-phase component and quadrature component, and the resultingsignals are then summed, block 166. The resulting DCS signal isconducted to bandpass filter 168, amplifier 170, and bandpass filter172. The RF signal thus produced is further conducted to the antenna 102via switch 180.

If the transmission is at the GSM frequency, the output signal of theGSM synthesizer is used as the mixing signal. The resultingcarrier-frequency signal is conducted to the GSM branch in which it isprocessed in the same manner as in the DCS branch blocks 186, 188, 190and 192. The RF signal thus produced is conducted to the antenna 102 viaswitch 180. One and the same antenna 102 can be used in bothtransmission and reception if the TX and RX circuits are coupled to theantenna through a duplex filter, for example. If the apparatus isdesigned to operate in two or more frequency bands, it needs separatefilters for each frequency band.

The circuit arrangement described above has, however, somedisadvantages. First, separate carrier-frequency signal branches in thereceiver and m the transmitter add to the complexity, size andmanufacturing costs of the transceiver. Second, each operating frequencyband needs a separate synthesizer of its own.

An object of the invention is to provide a simple solution for realizinga programmable transceiver operating in a plurality of systems in such amanner that the aforementioned disadvantages related to the prior artcan be avoided.

In the direct conversion based transceiver according to the inventionsignal processing can be performed using one and the same signalprocessing line regardless of the system. This is achieved using thesignal processing steps set forth below.

The method according to the invention for processing signals receivedfrom different radio interfaces of communication systems ischaracterized in that it comprises steps in which

-   -   a carrier-frequency signal is received from a radio interface,    -   the carrier-frequency signal is bandpass-filtered,    -   the filtered carrier-frequency signal is amplified,    -   an RX mixing signal at the receive frequency is generated,    -   a complex baseband signal is generated from the received        carrier-frequency signal by mixing it with the RX mixing signal,    -   the baseband signal generated is low-pass-filtered,    -   the baseband signal generated is amplified,    -   the baseband signal is converted digital, and    -   the baseband signal converted digital is processed to produce an        information signal encoded and modulated into the received        signal.

The method according to the invention for processing signals transmittedto different radio interfaces of communication systems is characterizedin that it comprises steps in which

-   -   a digital baseband quadrature signal is generated on the basis        of the information signal to be transmitted,    -   the digital baseband signal is converted analog,    -   a TX mixing signal at the transmit frequency is generated,    -   a carrier-frequency transmission signal is generated from the        baseband signal by mixing it with the TX mixing signal,    -   the carrier-frequency signal generated is amplified, and    -   the transmission signal is sent to the radio interface.

The direct-conversion receiver according to the invention operating atdifferent interfaces of communication systems is characterized in thatit comprises

-   -   antenna means for receiving a radio-frequency signal,    -   bandpass filter for filtering a carrier-frequency signal,    -   first RX amplifier for amplifying the filtered carrier-frequency        signal,    -   means for generating an RX mixing signal at the receive        frequency,    -   mixing means for generating a complex baseband signal from the        received signal        using me RX mixing signal,    -   low-pass filter for filtering the baseband signal,    -   second amplifier for amplifying the baseband signal,    -   analog-to-digital converter for converting the baseband signal        digital, and    -   means for processing the baseband signal converted digital to        produce an information signal encoded and modulated into the        received signal.

The direct-conversion transmitter according to the invention operatingat different radio interfaces of communication systems is characterizedin that it comprises

-   -   means for generating a digital baseband quadrature signal on the        basis of the information signal to be transmitted,    -   digital-to-analog converter for converting the baseband        transmission signal analog,    -   synthesizer for generating a TX mixing signal at the transmit        frequency,    -   mixing means for producing a signal at the carrier frequency        from the baseband        transmission signal using the TX mixing signal,    -   TX amplifier for amplifying the signal at the carrier frequency,        and    -   antenna means for transmitting the amplified transmission signal        at the carrier        frequency.

Other preferred embodiments of the invention are described in thedependent claims.

In the present invention, signal band limiting is advantageouslyperformed at the baseband frequency so that there is no need for “steep”filters and, therefore, system-specific filter lines. Filtering can thusbe performed as low-pass filtering using a filter with a controllablecut-off frequency. This way, it is possible to completely avoid separatesystem-specific channel filtering circuits.

To enable the generation of mixing frequencies of the differentoperating frequency bands by one and the same synthesizer it isadvantageously used frequency division of the synthesizer output signal.If the synthesizer's operating frequency is set higher than thefrequencies used in the systems, it is possible to generate, inconjunction with the synthesizer frequency division, two mixing signalswith a 90-degree phase difference, thus avoiding the need for phaseshifters on the signal line and achieving a good phase accuracy.

Using the solution according to the invention it is possible to realizea general-purpose transceiver which is considerably simpler and moreeconomical to manufacture than prior-art solutions. The circuitarrangement according to the invention requires only one TX signalbranch and one RX signal branch. Moreover, one and the same synthesizermay be used to generate the mixing signals. Furthermore, there is noneed for channel filters operating at the radio frequency. Therefore,the circuitry can be easily integrated. Since the invention involvesonly a few components, the advantages of the transceiver according tothe invention include small size and low power consumption.

The invention will now be described in more detail with reference to theaccompanying drawing wherein

FIG. 1 shows a block diagram of a dual-band direct-conversiontransceiver according to the prior art,

FIG. 2 shows in the form of block diagram a solution according to theinvention for a direct-conversion transceiver operating in multiplesystems.

FIG. 1 was already discussed in conjunction with the description of theprior art. Next, a transceiver according to the invention will bedescribed, referring to FIG. 2.

FIG. 2 shows in the form of block diagram a transceiver according to theinvention. A RF signal received through an antenna is conducted viamatching circuits 1 to controllable bandpass filter 2. The matchingcircuits 1 may advantageously be controllable (AX) with respect to theoperating frequency band. A controllable band-pass filter 2 may beadvantageously realized using a plurality of bandpass filters so thatthe RF signal is conducted via switch elements controlled by a controlsignal FX1 from the matching circuit 1 to the bandpass filter thatcorresponds to the selected operating frequency band. The bandpassfilter may also be realized so as to be adjustable and tuneable by meansor programming. The bandpass filtered carrier-frequency signal isfurther conducted to a low-noise amplifier 4, the gain of which isadvantageously controllable. The control signal is marked GX1 in thedrawing. In addition to amplifier 4, it is also possible to haveintegrated amplifiers in connection with the bandpass filters.

The signal is then conducted to a mixer 5 in which the carrier-frequencysignal is mixed with an RX mixing signal at the receive frequency toproduce a baseband quadrature signal. The RX mixing signal isadvantageously generated by a synthesizer 10 the output signal frequencyof which is divided by a divider 11 so as to correspond to the selectedreceive frequency. The synthesizer 10 operates in a similar manner asthe synthesizers depicted in FIG. 1. Thus it comprises avoltage-controlled oscillator VCO which produces an output signal. Thefrequency of the VCO output signal is divided by S1 in a divider in thephase locked loop PLL. The resulting signal is conducted to a firstinput of a phase comparator in the phase-locked loop. Similarly, thefrequency of a signal generated by a reference oscillator in thephase-locked loop PLL is divided by an integer and conducted to a secondinput of the phase comparator. The phase comparator produces a signalwhich is proportional to the phase difference of the two input signalsand conducted to a low-pass filter, and the filtered signal thencontrols the voltage-controlled oscillator VCO. The output frequency iscontrolled by varying the divisor S1.

The synthesizer output signal is divided in divider 11 by N1 so that theRX mixing signal corresponds to the selected receive frequency band. Theoutput frequency of the synthesizer may be e.g. in the 4 GHz band, sothat with 2-GHz systems the synthesizer output frequency is divided bytwo, and with 1-GHz systems it is divided by four (N1). This way,systems operating in the 1-GHz and 2-GHz bands can be covered with asynthesizer the operating frequency band of which is narrow with respectto the operating frequency.

To produce a quadrature baseband signal the mixer needs two mixingsignals with a phase shift of 90 degrees. Phase-shifted components maybe produced by a phase shifter in connection with the mixer or they maybe produced as quotients generated already in the frequency divider 11,thus achieving an accurate phase difference. Therefore, it isadvantageous to use a synthesizer operating frequency which is amultiple of the highest system frequency.

The in-phase component 1 and quadrature component Q from the mixer 5 arefurther conducted to low-pass filters 6. The higher cut-off frequency ofthe low-pass filters is advantageously controllable with control signalFX3. Thus the filtering can be performed at a bandwidth corresponding tothe selected radio interface, and since the filtering is performed atbaseband, it is easy to get the filtering function steep. Also, nostrict demands are set on the bandpass filtering (2) of the RF signal.

The baseband signal is further conducted to a gain control block 7 whichpossibly includes an offset voltage correction block. On the other hand,considering the broad bandwidth of the CDMA system, the offset voltagecan easily be removed by high-pass filtering. The amplifieradvantageously realizes automatic gain control (AGC). Finally, thesignal is convened digital in an analog-to-digital converter 8, and thedigital baseband signal is further processed in a digital signalprocessor (DSP) 9. Channel filtering may also be performed digitally inthe DSP, whereby the low-pass filtering of the baseband signal may beperformed using a fixed cut-off frequency. Then, however, the dynamicsof the analog-to-digital converter must be considerably better.

In the transmitter part, a quadrature baseband signal is first digitallygenerated in block 9 on the basis of the information signal to be sent.The components of the digital signal are converted analog bydigital-to-analog converters 14, whereafter the analog signals arelow-pass filtered by low-pass filters 15. Advantageously, the cutofffrequency of the low-pass filters can be controlled with control signalFX4 so as to correspond to the specifications of the selected radiointerface.

A TX mixing signal at the carrier frequency is generated by asynthesizer 13 and divider 12. The synthesizer 13 operates in a similarmanner as the synthesizer 10 in the receiver pan. Moreover, thesynthesizers may share a reference oscillator. The frequency of thesynthesizer output signal is controlled with control signal S2 withinthe synthesizer's operating frequency range. The frequency of the outputsignal from synthesizer 13 is divided in divider 12 so as to correspondto the selected transmission frequency band. Components phase-shifted by90 degrees are generated from the TX mixing signal in order to performcomplex mixing in mixer 16. The phase-shifted components may begenerated in the same way as in the receiver part.

The signal at the carrier frequency is then amplified in an amplifier17, the gain of which is advantageously controllable in order to set thetransmission power and realize automatic gain control (AGC). The controlsignal is marked GX3 in FIG. 2. The signal is then conducted to a poweramplifier 18. The operating frequency band of the power amplifier isadvantageously selectable with control signal BX. This can be achievede.g. such that the amplifier comprises partly separate signal lines forthe different operating frequency bands.

The RF signal generated is filtered by a bandpass filter 3. The passband of the bandpass filter is advantageously controllable with controlsignal FX2. This can be realized in the same way as in the receiverpart. The receiver and transmitter part filters 2 and 3 areadvantageously realized in duplex filter pairs for each transmit-receivefrequency band associated with a given system. The filters mayadvantageously be surface acoustic wave (SAW) or bulk acoustic wave(BAW) filters so that several filters with their switches may beattached to one component.

The control signals in the mobile station transceiver according to FIG.2 are preferably generated in a control block of the mobile stationwhich advantageously comprises a processing unit such as amicroprocessor. The control block generates the signal on the basis of asystem switch instruction input from the keypad of the mobile station,for example. System selection may be e.g. menu-based so that the desiredsystem is selected by choosing it from a displayed menu by pressing acertain key on the keypad. The control block then generates the controlsignals that correspond to the selected system. The system switchinstruction may also come via the mobile communication system in such amanner that data received from the system may include a system switchinstruction on the basis of which the control block performs the systemswitch. Advantageously, a control program is stored in a memory unitused by the control block, which control program monitors the receiveddata and, as it detects a system switch instruction in the data, givesthe control block an instruction to set the control signals into statesaccording to the selection instruction.

The implementation of the blocks described above is not illustrated inmore detail as the blocks can be realized on the basis of theinformation disclosed above, applying the usual know-how of a personskilled in the art.

Above it was described embodiments of the solution according to theinvention. Naturally, the principle according to the invention may bemodified within the scope of the invention as defined by the claimsappended hereto, e.g. as regards implementation details and fields ofapplication. It is especially noteworthy that the solution according tothe invention may be well applied to communication systems other thanthe mobile communication systems mentioned above. Apart from thecellular radio interface proper, the solution may be used to realizee.g. a GPS receiver for the location of a mobile station or otherapparatus. Furthermore, the operating frequencies mentioned are given byway of example only, and the implementation of the invention is in noway restricted to them.

It is also noteworthy that the solution according to the invention maybe applied to all current coding techniques such as the narrow-band FDMA(Frequency Division Multiple Access) and TDMA (Time Division MultipleAccess), as well as me broadband CDMA (Code Division Multiple Access)technique. In addition, the solution according to the invention may beused to realize an FM (Frequency Modulation) receiver.

Below is a table listing some of the so-called second generation mobilecommunication systems to which the present invention may be applied. Thetable shows the most important radio interface related characteristicsof the systems.

GSM PDC DECT Digital PHS Personal Global System Personal European HandyCELLULAR IS-95 US for Mobile Digital Cordless Phone SYSTEM AMPSIS-54/-136 CDMA Communications DCS 1800 Cellular Telephone System RXFREQ. 869-894 869-894 869-894 935-960 1805-1880  810-826, 1880-19001895-1918 (MHz) 1429-1453 TX FREQ. 824-849 824-849 824-849 890-9151710-1785 940-956 1880-1900 1895-1918 (MHz) 1477-1501 RF BAND- 25 MHz 25MHz 25 MHz 25 MHz 75 MHz 16 MHz 20 MHz 23 MHz WITH 24 MHz MULTIPLE FDMATDMA/ CDMA/ TDMA/ TDMA/ TDMA/ TDMA/ TDMA/ ACCESS FDMA FDMA FDMA FDMAFDMA FDMA FDMA METHOD DUPLEX FDD FDD FDD FDD FDD FDD TDD TDD METHODNUMBER OF 832 832, 20, 124, 374, 1600, 10, 300, CHANNELS 3 users/ 798users/ 8 users/ 8 users/ 3 users/ 12 users/ 4 users/ channel channelchannel channel channel channel channel CHANNEL 30 KHz 30 kHz 1250 kHz200 kHz 200 kHz 25 kHz 1,728 MHz 300 kHz SPACING MODULATION FM π/4DQPSKQPSK/ GMSK 0.3 GMSK 0.3 π/4 DQPSK GFSK 0.3 π/4 DQPSK OQPSK GaussianGaussian Gaussian filter filter filter CHANNEL — 48.6 kb/s 1.2288 Mb/s270.833 kb/s 270.833 kb/s 42 kb/s 1.152 MB/S 384 kb/s BIT RATE

Below is another table listing some of the so-called third generationmobile communication systems to which the present invention may beapplied. The table shows the most important radio interface relatedcharacteristics of the system.

CELLULAR SYSTEM WCDMA RX FREQ. (MHz) 2110-2170 1900-1920 TX FREQ. (MHz)1920-1980 1900-1920 MULTIPLE ACCESS CDMA TDMA METHOD DUPLEX METHOD FDDTDD CHANNEL SPACING 5 MHz 5 MHz MODULATION QPSK CHANNEL BIT RATE 144kb/s in rural outdoor, 500 kb/s in urban outdoor and up to 2 Mb/s inindoor

The invention claimed is:
 1. A direct-conversion transceiver capable ofoperating with different radio interfaces including a first radiointerface conforming to a code division multiple access (CDMA) systemand a second radio interface conforming to a time division multipleaccess (TDMA) system, comprising: a first controllable bandpass filterconfigured to filter a received signal using one of a first plurality ofpassbands selected according to at least one control signalcorresponding to a selected one of the different radio interfaces,wherein the first controllable bandpass filter has a signal path commonto both the first radio interface and the second radio interface; alow-noise amplifier configured to amplify the filtered received signalaccording to the at least one control signal corresponding to theselected one of the different radio interfaces, which controls an amountof gain, wherein the low-noise amplifier has a signal path common toboth the first radio interface and the second radio interface; a firstprogrammable synthesizer configured to generate a first mixing signalaccording to the at least one control signal corresponding to theselected one of the different radio interfaces, wherein the firstprogrammable synthesizer has a signal path common to both the firstradio interface and the second radio interface; a first frequencydivider coupled to the first programmable synthesizer and configured todivide a first frequency of the first mixing signal by two to provide afirst divided frequency signal according to the at least one controlsignal corresponding to the selected one of the different radiointerfaces; a first mixer coupled to the low-noise amplifier andconfigured to mix the amplified and filtered received signal with thefirst divided frequency signal to produce a first baseband quadraturesignal, wherein the first mixer has a signal path common to both thefirst radio interface and the second radio interface and wherein thefirst mixer produces the first baseband quadrature signal on the basisof two 90-degree phase-shifted first components produced from the firstfrequency divider and is operable to process either a TDMA signal or aCDMA signal; a first low-pass filter coupled to the first mixer andconfigured to low-pass filter the first baseband quadrature signalaccording to the at least one control signal corresponding to theselected one of the different radio interfaces, wherein the firstlow-pass filter has a signal path common to both the first radiointerface and the second radio interface and is operable to processeither the TDMA signal or the CDMA signal; a first gain-controlledamplifier coupled to the first low-pass filter and configured to providegain-controlled amplification of the low-pass filtered first basebandquadrature signal, wherein the first gain-controlled amplifier has asignal path common to both the first radio interface and the secondradio interface and is operable to process either the TDMA signal or theCDMA signal; an analog-to-digital converter coupled to the firstgain-controlled amplifier and configured to convert to digital form anoutput of the first gain-controlled amplifier; a digital signalprocessor configured to receive digital output from theanalog-to-digital converter and to further process said digital output;a digital-to-analog converter coupled to the digital signal processorand configured to receive a second baseband quadrature signal from thedigital signal processor and to provide analog output signals; a secondlow-pass filter coupled to the digital-to-analog converter andconfigured to low-pass filter the analog output signals from thedigital-to-analog converter according to the at least one control signalcorresponding to the selected one of the different radio interfaces,wherein the second low-pass filter has a signal path common to both thefirst radio interface and the second radio interface and is operable toprocess either the TDMA signal or the CDMA signal; a second programmablesynthesizer configured to generate a second mixing signal according tothe at least one control signal corresponding to the selected one of thedifferent radio interfaces, wherein the second programmable synthesizerhas a signal path common to both the first radio interface and thesecond radio interface; a second frequency divider coupled to the secondprogrammable synthesizer and configured to divide a second frequency ofthe second mixing signal by two to provide a second divided frequencysignal according to the at least one control signal corresponding to theselected one of the different radio interfaces; a second mixer coupledto the second low-pass filter and configured to mix signals from thesecond low-pass filter and the second frequency divider to produce acarrier-frequency transmission signal, wherein the second mixer has asignal path common to both the first radio interface and the secondradio interface and wherein the second mixer produces thecarrier-frequency transmission signal on the basis of two 90-degreephase-shifted second components produced from the second frequencydivider and is operable to process either the TDMA signal or the CDMAsignal; a second gain-controlled amplifier coupled to the second mixerand configured to control gain according to the at least one controlsignal corresponding to the selected one of the different radiointerfaces, wherein the second gain-controlled amplifier has a signalpath common to both the first radio interface and the second radiointerface and is operable to process either the TDMA signal or the CDMAsignal; a power amplifier coupled to the second gain-controlledamplifier and configured to produce an amplified output using afrequency band determined on the basis of the at least one controlsignal corresponding to the selected one of the different radiointerfaces, wherein the power amplifier has a signal path common to boththe first radio interface and the second radio interface; a secondcontrollable bandpass filter configured to filter the amplified outputof the power amplifier with one of a second plurality of passbandsselected according to the at least one control signal corresponding tothe selected one of the different radio interfaces, and wherein thesecond controllable bandpass filter has a signal path common to both thefirst radio interface and the second radio interface; and amicroprocessor configured to generate the at least one control signal tocause selection of the selected one of the different radio interfaces.2. The direct-conversion transceiver of claim 1, wherein the codedivision multiple access (CDMA) system is a WCDMA system and the timedivision multiple access (TDMA) system is a Global System for Mobilecommunications (GSM) system.
 3. An apparatus comprising: adirect-conversion transmitter configured to transmit radio-frequencysignals of mobile communication systems using a plurality of radiointerfaces; wherein the direct-conversion transmitter comprises: adigital-to-analog converter configured to convert a digital basebandquadrature signal to an analog baseband transmission signal; a transmitsynthesizer common to the plurality of radio interfaces and configuredto generate a mixing signal; a controllable low-pass filter configuredto perform channel filtering of the analog baseband transmission signalusing a controllable cut-off frequency to produce a low-pass filteredsignal, wherein the controllable cut-off frequency corresponds to whichone of the plurality of radio interfaces is selected, and wherein thecontrollable low-pass filter is configured to filter the analog basebandtransmission signal through a common signal path that is used for eachof the plurality of radio interfaces; a frequency divider common to theplurality of radio interfaces and configured to divide a frequency ofthe mixing signal at least by two, wherein the dividing produces twomixing signal components having a 90-degree phase difference; a mixercommon to the plurality of radio interfaces and configured to produce acarrier-frequency signal based on the low-passed filtered signal and thetwo mixing signal components; and a controllable gain transmitteramplifier common to the plurality of radio interfaces and configured toamplify the carrier-frequency signal at a gain controlled according towhich one of the plurality of radio interfaces is selected, wherein atleast one of the plurality of radio interfaces includes at least onemodulation type and at least one channel bit rate that at least oneother of the plurality of radio interfaces does not have.
 4. Theapparatus of claim 3, wherein the controllable gain transmitteramplifier is configured to perform automatic gain control.
 5. Theapparatus of claim 3, further comprising: a bandpass filter configuredto filter the carrier-frequency signal amplified by the controllablegain transmitter amplifier, and including a selectable pass band setaccording to which one of the plurality of radio interfaces is selected.6. The apparatus of claim 3, wherein at least two of the plurality ofradio interfaces have different transmission frequencies.
 7. Theapparatus of claim 3, further comprising a control block circuitconfigured to generate at least one control signal that indicates whichof the plurality of radio interfaces is selected.
 8. The apparatus ofclaim 3, further comprising a power amplifier configured to furtheramplify the carrier-frequency signal amplified by the controllable gaintransmitter amplifier and having a controllable operating frequency bandset according to which one of the plurality of radio interfaces isselected.
 9. The apparatus of claim 3, further comprising a directconversion receiver comprising: a bandpass filter configured to filter areceived second carrier-frequency signal, a first receiver amplifierconfigured to amplify the received second carrier-frequency signalfiltered by the bandpass filter, a receiver synthesizer configured togenerate a receiver mixing signal at a receive frequency, a receivermixer configured to generate a complex baseband signal by mixing thereceiver mixing signal with the received second carrier-frequency signalamplified by the first receiver amplifier, a receiver low-pass filterconfigured to filter the complex baseband signal, a second receiveramplifier configured to amplify the complex baseband signal filtered bythe receiver low-pass filter, and an analog-to-digital converterconfigured generate a receiver digital baseband signal by converting thecomplex baseband signal amplified by the second receiver amplifier todigital form.
 10. The apparatus of claim 3, wherein a first radiointerface of the plurality of radio interfaces employs a WCDMA systemand a second radio interface of the plurality of radio interfacesemploys a Global System for Mobile communications (GSM) system.
 11. Theapparatus of claim 3, wherein at least one of the plurality of radiointerfaces includes at least one multiple access method that at leastone other of the plurality of radio interfaces does not have.
 12. Theapparatus of claim 11, wherein the plurality of radio interfaces furtherdiffer from each other by at least channel spacing.
 13. The apparatus ofclaim 12, wherein the plurality of radio interfaces further differ fromeach other by at least duplex method.
 14. The apparatus of claim 13,wherein the plurality of radio interfaces further differ from each otherby at least RF bandwidth.
 15. The apparatus of claim 11, wherein theplurality of radio interfaces further differ from each other by at leastduplex method.
 16. The apparatus of claim 11, wherein the plurality ofradio interfaces further differ from each other by at least RFbandwidth.
 17. The apparatus of claim 3, wherein the plurality of radiointerfaces further differ from each other by at least multiple accessmethod.
 18. The apparatus of claim 17, wherein the plurality of radiointerfaces further differ from each other by at least channel spacing.19. The apparatus of claim 18, wherein the plurality of radio interfacesfurther differ from each other by at least duplex method.
 20. Theapparatus of claim 19, wherein the plurality of radio interfaces furtherdiffer from each other by at least RF bandwidth.
 21. The apparatus ofclaim 17, wherein the plurality of radio interfaces further differ fromeach other by at least duplex method.
 22. The apparatus of claim 17,wherein the plurality of radio interfaces further differ from each otherby at least RF bandwidth.
 23. The apparatus of claim 3, wherein theplurality of radio interfaces further differ from each other by at leastchannel spacing.
 24. The apparatus of claim 23, wherein the plurality ofradio interfaces further differ from each other by at least duplexmethod.
 25. The apparatus of claim 23, wherein the plurality of radiointerfaces further differ from each other by at least RF bandwidth. 26.The apparatus of claim 3, wherein the plurality of radio interfacesfurther differ from each other by at least duplex method.
 27. Theapparatus of claim 26, wherein the plurality of radio interfaces furtherdiffer from each other by at least RF bandwidth.
 28. The apparatus ofclaim 3, wherein the plurality of radio interfaces further differ fromeach other by at least RF bandwidth.
 29. The apparatus of claim 3,wherein at least two of the plurality of radio interfaces have a commontransmission frequency.
 30. The apparatus of claim 3, wherein at leasttwo of the plurality of radio interfaces have a common transmissionfrequency range.
 31. The apparatus of claim 3, wherein at least two ofthe plurality of radio interfaces have at least partially overlappingtransmission frequency ranges.
 32. The apparatus of claim 3, wherein atleast two of the plurality of radio interfaces have transmissionfrequency ranges that are adjacent to each other.
 33. The apparatus ofclaim 3, wherein at least two of the plurality of radio interfaces havetransmission frequency ranges separated by about 41 MHz.
 34. Theapparatus of claim 3, wherein at least two of the plurality of radiointerfaces have transmission frequency ranges separated by about 2 MHz,20 MHz, 91 MHz, 135 MHz, 419 MHz, 628 MHz, 861 MHz, 964 MHz, 1005 MHz,1031 MHz, 1046 MHz, 1051 MHz, or 1071 MHz.
 35. The apparatus of claim 3,wherein a separation of respective transmission frequency bands of atleast two of the plurality of radio interfaces ranges from about 2 MHzto about 1071 MHz.
 36. The apparatus of claim 3, further comprising adirect-conversion receiver configured to receive a secondcarrier-frequency signal and produce, based on which one of theplurality of radio interfaces is selected, an analog baseband receptionsignal by direct conversion of the second carrier-frequency signal. 37.The apparatus of claim 3, wherein a first radio interface of theplurality of radio interfaces employs a TDMA multiple access method anda second radio interface of the plurality of radio interfaces employs aCDMA multiple access method.
 38. A method comprising: transmittingradio-frequency signals through direct conversion and using a pluralityof radio interfaces of mobile communication systems; wherein thetransmitting through direct conversion includes: converting a digitalbaseband quadrature signal to an analog baseband transmission signal;low-pass filtering the analog baseband transmission signal using acontrollable cut-off frequency to produce a low-pass filtered signal,wherein the controllable cut-off frequency is corresponds to which oneof the plurality of radio interfaces is selected, wherein the low-passfiltering of the analog baseband transmission signal occurs through acommon signal path that is used for each of the plurality of radiointerfaces; generating a mixing signal at a transmission frequency usinga transmit synthesizer common to the plurality of radio interfaces;dividing a frequency of the mixing signal at least by two with afrequency divider common to the plurality of radio interfaces, thedividing producing two mixing signal components having a 90-degree phasedifference; generating, with a mixer common to the plurality of radiointerfaces, a carrier-frequency signal based on the low-pass filteredsignal and the two mixing signal components; and amplifying thecarrier-frequency signal using a controllable gain transmitter amplifiercommon to the plurality of radio interfaces at a gain controlledaccording to which one of the plurality of radio interfaces is selected,wherein at least one of the plurality of radio interfaces includes atleast one modulation type and at least one channel bit rate that atleast one other of the plurality of radio interfaces does not have. 39.The method of claim 38, wherein each of the plurality of radiointerfaces operates at a different transmission frequency.
 40. Themethod of claim 38, further comprising: performing automatic gaincontrol with the controllable gain transmitter amplifier.
 41. The methodof claim 38, further comprising: bandpass filtering thecarrier-frequency signal amplified by the controllable gain transmitteramplifier using a selectable pass band set according to which one of theplurality of radio interfaces is selected.
 42. The method of claim 38,further comprising: amplifying the carrier-frequency signal amplified bythe controllable gain transmitter amplifier with a power amplifierhaving a controllable operating frequency band determined according towhich one of the plurality of radio interfaces is selected.
 43. Themethod of claim 38, wherein a first radio interface of the plurality ofradio interfaces employs a WCDMA system and a second radio interface ofthe plurality of radio interfaces employs a Global System for Mobilecommunications (GSM) system.
 44. The method of claim 38, furthercomprising generating at least one control signal that indicates whichof the plurality of radio interfaces is selected.
 45. The method ofclaim 38, wherein at least one of the plurality of radio interfacesincludes at least one multiple access method that at least one other ofthe plurality of radio interfaces does not have.
 46. The method of claim45, wherein the plurality of radio interfaces further differ from eachother by at least channel spacing.
 47. The method of claim 46, whereinthe plurality of radio interfaces further differ from each other by atleast duplex method.
 48. The method of claim 47, wherein the pluralityof radio interfaces further differ from each other by at least RFbandwidth.
 49. The method of claim 45, wherein the plurality of radiointerfaces further differ from each other by at least duplex method. 50.The method of claim 45, wherein the plurality of radio interfacesfurther differ from each other by at least RF bandwidth.
 51. The methodof claim 38, wherein the plurality of radio interfaces further differfrom each other by at least multiple access method.
 52. The method ofclaim 51, wherein the plurality of radio interfaces further differ fromeach other by at least channel spacing.
 53. The method of claim 52,wherein the plurality of radio interfaces further differ from each otherby at least duplex method.
 54. The method of claim 53, wherein theplurality of radio interfaces further differ from each other by at leastRF bandwidth.
 55. The method of claim 51, wherein the plurality of radiointerfaces further differ from each other by at least duplex method. 56.The method of claim 51, wherein the plurality of radio interfacesfurther differ from each other by at least RF bandwidth.
 57. The methodof claim 38, wherein the plurality of radio interfaces further differfrom each other by at least channel spacing.
 58. The method of claim 57,wherein the plurality of radio interfaces further differ from each otherby at least duplex method.
 59. The method of claim 57, wherein theplurality of radio interfaces further differ from each other by at leastRF bandwidth.
 60. The method of claim 38, wherein the plurality of radiointerfaces further differ from each other by at least duplex method. 61.The method of claim 60, wherein the plurality of radio interfacesfurther differ from each other by at least RF bandwidth.
 62. The methodof claim 38, wherein the plurality of radio interfaces further differfrom each other by at least RF bandwidth.
 63. The method of claim 38,wherein at least two of the plurality of radio interfaces have a commontransmission frequency.
 64. The method of claim 38, wherein at least twoof the plurality of radio interfaces have a common transmissionfrequency range.
 65. The method of claim 38, wherein at least two of theplurality of radio interfaces have at least partially overlappingtransmission frequency ranges.
 66. The method of claim 38, wherein atleast two of the plurality of radio interfaces have transmissionfrequencies that are adjacent to each other.
 67. The method of claim 38,wherein at least two of the plurality of radio interfaces havetransmission frequency ranges separated by about 41 MHz.
 68. The methodof claim 38, wherein at least two of the plurality of radio interfaceshave transmission frequency ranges separated by about 2 MHz, 20 MHz, 91MHz, 135 MHz, 419 MHz, 628 MHz, 861 MHz, 964 MHz, 1005 MHz, 1031 MHz,1046 MHz, 1051 MHz, or 1071 MHz.
 69. The method of claim 38, wherein aseparation of respective transmission frequency bands of at least two ofthe plurality of radio interfaces ranges from about 2 MHz to about 1071MHz.
 70. The method of claim 38, further comprising receiving a secondcarrier-frequency signal and producing, based on which one of theplurality of radio interfaces is selected, an analog baseband receptionsignal by direct conversion of the second carrier-frequency signal. 71.The method of claim 38, wherein a first radio interface of the pluralityof radio interfaces employs a TDMA multiple access method and a secondradio interface of the plurality of radio interfaces employs a CDMAmultiple access method.